The invention disclosed herein relates to charging dry cell batteries, particularly of the alkaline type which are considered non-rechargeable by consumers and now are discarded after the first time they run down. The invention has particular application to recharging 1.5 volt batteries of sizes N, AAA, AA, C and D.
Alkaline manganese dioxide zinc batteries, commonly referred to simply as "alkaline" batteries, e.g., 1.5 volt cells sold under the trademarks DURACELL and EVEREADY ENERGIZER, today are used in thousands of applications from toys, electronics and cameras to flashlights. They are accepted as "single use" batteries, i.e., they are not thought to be rechargeable and are thrown away when they run down. (Battery manufacturers have long known that secondary alkaline batteries are safely rechargeable. For example, see pages 275-281 and 291-301 of Eveready Battery Applications Engineering, 1971.) Even though not considered by most people to be rechargeable, alkaline primary batteries are preferred over rechargeable nickel cadmium ("Ni--Cad") batteries and the older zinc-based batteries because they typically last several times longer, do not contain acid which in the zinc-based cells are prone to leaking, work well with high current drain devices (unlike the Ni--Cad batteries), are much cheaper than Ni--Cad batteries and are also cheaper than zinc-based batteries on a per-unit of power delivered basis, withstand the cold best and have the longest shelf life. Though rechargeable, Ni--Cad batteries are only rated at 1.25 volts when new, as compared to a 1.5 volt rating for alkaline batteries, and the capacity of Ni--Cad batteries decreases with repeated recharging. Ni--Cad batteries also give little or no warning when they are about to run out, which poses problems in portable computer applications. The superiority of alkaline batteries over Ni--Cad and zinc-based batteries is reflected in their respective sales. The size of the U.S. market is thought to easily exceed one billion dollars annually, two-thirds of which is alkaline battery sales.
Despite the overwhelming superiority of alkaline batteries, and the fact that they are known by those skilled in the battery art to be rechargeable, as far as the applicant is aware, there is no commercially available alkaline battery charger; therefore, they all end up in the trash after a single use. Not only do the millions of discarded alkaline batteries form a source of heavy metal environmental pollution, but they needlessly cost consumers millions of dollars a year in replacement batteries.
The Eveready publication, cited above, discloses a method and a charging circuit for recharging alkaline manganese dioxide zinc batteries. The patent literature also discloses methods and charging circuits for recharging batteries which were generally accepted by consumers as being non-rechargeable. The following disclose methods and circuits for charging alkaline batteries: International PCT Publication WO 91/07000 (published May 16. 1991, Szorady et al.), and U.S. Pat. Nos. 4,308,493 (Kothe et al.), 4,031,450 (Hammel et al.) and 3,735,232 (Fister). U.S. Pat. No. 4,629,963 (Morris) discloses a method and circuit for recharging dry cells "that once discharged . . . are normally replaced." The following disclose methods and circuits for recharging zinc-based batteries: U.S. Pat. Nos. 3,556,849 (Oswin et al.), 3,563,800 (Oswin et al.) and 2,369,033 (Eubank). U.S. Pat. No. 3,081,366 (Belove) discloses a sealed, rechargeable alkaline battery with an automatic charging cut-off circuit within the battery.
The patent literature discloses many battery charging methods and circuits for charging Ni--Cad and other batteries which use many different techniques and circuits. Recently, battery charging circuits have been disclosed which are microprocessor controlled. See, for example, U.S. Pat. No. 5,055,763 (Johnson et al.).
There is, however, a need for a battery charging method and charger which safely recharges alkaline batteries, and which preferably recharges Ni--Cad and zinc based batteries as well, and for a battery charger particularly for recharging alkaline batteries which is relatively simple and inexpensive to manufacture. There is also a need for such a battery charger which accepts different size batteries for recharging (for example, N, AAA, AA, C and D), so that the same recharger may be used to recharge all or most of the batteries used in a typical household, office, etc.